[Draft] Directory parsing home crate

[Cloud0310]

• added customized upstream home crate APIs: {CARGO,RUSTUP}_{CACHE,DATA,CONFIG,STATE}_HOME
• platform dir parsing code for Unix, windows still needs further refine, has a prototype that's not refactored with new commit for now
• testing out dir parsing cases: relative, missing, unset as missing, and normal parsing aligned with xdg specification
• pre-RFC guided tests about new behavior, roughly order is: split > legacy > platform